In high pressure fluid systems such as are common in hydrocarbon exploration and recovery, pressure differences between parts of a system can be extremely large which can prevent valves opening easily. It can also be unsafe to open valves, particularly large valves, across which there is a very high pressure differential because the sudden change in pressure can cause failures in seals or in other components of such systems. Preferably pressure differences in high pressure systems are kept within specified limits and thus there is a need for improved methods and apparatus for accurately and reliably regulating pressure in parts of a system.
There is a particular need for accurate and highly controllable pressure regulation in subsea pump systems which are filled with barrier fluids at a higher pressure than the process fluids they are pumping so as to prevent process fluid leaking out. Instead barrier fluid will bleed through seals into the process fluid. The pressure of the barrier fluid must be carefully controlled and kept within a predetermined pressure envelope, i.e. between safe minimum and maximum values.
In subsea systems such pressure regulation is usually effected from the surface through an umbilical and therefore there can be a time delay involved, especially in deep water high pressure offshore hydrocarbon field developments which are becoming more common. This delay makes it more difficult to effectively control pressures.
It is also sometimes desired to take measurements or perform tests at particular pressures and hence it is desirable to be able to adjust the pressure in a system in a controlled manner so as to achieve and maintain the desired pressure accurately.